1. Field of the Invention
The present invention relates to a digital signal reproduction circuit and a digital signal reproduction method and particularly, to a digital signal reproduction circuit and a digital signal reproduction method in which a signal supplied is waveform-equalized so as to reproduce the digital signal and a synchronization clock of this digital signal.
2. Description of the Prior Art
For example, in an optical disc reproduction apparatus, an optical-magnetic disc reproduction apparatus or the like, a signal reproduced from an optical pickup is converted into binary data so as to generate a digital signal and a synchronous signal which is synchronized with this digital signal. Especially when reproducing a recording medium in which data is recorded with a high density, a signal reproduced from the optical pickup is waveform-equalized and after this, the data is converted into a binary data, so as to generate a digital signal or the like. The reason why this waveform equalization is carried out is that the signal to be reproduced from the recording medium of a high density has a band up to the vicinity of a spatial shield frequency and contains data having sign components which may interfere with one another. This sign interference can be eliminated by the waveform equalization, and a digital signal generated has less errors, enabling to reproduce a data correctly.
The waveform equalization is realized by a waveform equalization circuit having a predetermined transfer function. In general, the transfer function of the waveform equalization circuit is adjusted, before shipment, according to the optical pickup characteristics, and after shipment, the transfer function is fixed to this adjustment without being changed.
However, the optimal value of the transfer function of the waveform equalization circuit depends on the optical pickup characteristics and a recording condition of a signal recorded in a recording medium. Consequently, if this transfer function of the waveform equalization circuit is fixed to a certain value, it is impossible to obtain an optimal value in accordance with a change of characteristics caused by a temperature change or simply by a time lapse and a difference in the signal recording condition caused by the recording medium. Therefore, in the where case the transfer function is fixed, reproduced data may have a deteriorated quality with a higher error rate depending on the reproduction condition.